This invention relates to an improved process for preparing linear condensation polyesters. More particularly, it relates to an improved process for preparing high molecular weight and high quality linear condensation polyesters or copolyesters suitable for processing into fibers, filament, films and other shaped articles as a continuous or discontinuous process.
Linear condensation polyester is prepared by a two-stage process, namely, the first stage of preparing monomeric bis-glycol ester of polycarboxylic acid or its oligomer, and the second stage of subjecting the product to further polycondensation.
Even more particularly, this invention relates to a catalyst for both esterification and polycondensation in the preparation of polyesters.
Many titanium catalysts, including diisopropyl di-triethanolamine ortho-titanate, hereinafter called triethanolamine titanium chelate, (available under the duPont tradename .-+.Tyzor" TE) have been used for esterification. In the direct esterification of terephthalic acid with ethylene glycol it has been necessary in the past to add ether inhibitors along with the catalyst to suppress undesirable side reactions which form diethylene glycol (DEG) which is incorporated as ether linkages in the polymer chains. The presence of ether linkages lowers the melting point of the polymer and makes it more sensitive towards light and heat degradation. The ether inhibitors used are generally basic compounds such as alkyl amines; their use not only involves extra expense but they cause additional processing problems.